The present invention relates to an electropneumatic horn particularly adapted to equip two- and four-wheeled motor vehicles.
The electropneumatic horns of the prior art comprise a generator of sound waves including one or more acoustic units, connected to an electric compressor by ducts for air passage to generate a mono, bi o tri tonal tuned sound according to the number of acoustic units.
More particularly the acoustic units consist of a straight exponential duct of a length proportional to the frequency to be reproduced, inserted in an acoustic chamber in which a membrane free to move with a reciprocating motion is arranged.
The straight duct comprises a first stretch with generally constant section, provided with an inlet mouth for the sound signal generated by the oscillating membrane and a second stretch having a section varying with a generally conic exponential law ending with an outlet mouth for the amplified sound signal.
The membrane is properly stretched in a calibration phase by deformation against said membrane of a metal member referred to as bottom and applied to the shape of chamber body, in such a way to generate a sound with predetermined acoustic pressure.
In a different constructional version of the prior art the acoustic units are two and the corresponding ducts are volute wound and juxtaposed to limit the overall dimensions of the horn.
As already stated said acoustic horns and more particularly those with a straight acoustic units, equip motor vehicles and are generally installed in the engine compartments.
Acoustic horns with different features are available on the market, mainly classified according to the number of acoustic units, generally one to maximum three for the tuned sound, and according to the frequency that each unit should reproduce.
The need to optimise space and reduce dimensions of every element of the motor vehicle, led to reduce as much as possible the dimensions of the acoustic horns by miniaturization of the compressor assembly and the assembly comprising the acoustic units.
The solutions proposed up to now did not lead to great results, mainly in view of the correlation existing between the required sound frequency and required duct lengths, as well as the number of acoustic units anyway indispensable to reproduce simultaneously more frequencies.
With regard to installation of said acoustic horns, the compressor and the acoustic units are individually anchored to opposite supports through corresponding fastening members.
The compressor is then connected to each acoustic unit through a rubber duct provided with deviations allowing to convey compressed air in each acoustic chamber of the acoustic units.
A first drawback of such horns consists of the assembling complexity in the installation phase because bracketing of two or more components corresponding to the compressor and the acoustic units is required.
Another drawback consists in that the connection between each acoustic unit and the compressor is difficult and time consuming and does not warrant when improperly effected, instantaneousness and contemporaneousness of sound of the acoustic units.
As a matter of fact it is often impossible to carry out a correct assembly, more particularly with regard to the air connection between compressor and sound wave generator, thus making impossible to mount in limited space several components divided from each other but at the same time requiring to be installed close to each other to obtain sound instantaneousness and with the acoustic ducts being equidistant from the compressor to warrant contemporaneousness of sound.
In order to remove this drawback electromagnetic horns are widely used, warranting a good response to actuation and having a compact structure as well.
However, the assembling phase of said electromagnetic horns requires the use of special brackets, which are essential for their operation and have the drawback of increasing the overall dimensions of the assembly.